The present invention relates generally to a burner control system of the type such as may be utilized in home furnaces and water heaters to provide for intermittent burning of fuel in order to maintain a desired temperature level. More particularly, the present invention relates to a burner control system including a pump for delivering the fuel under pressure to a pressure regulating valve and then through a fuel line leading from the regulating valve to a burner nozzle where combustion occurs. The flow of fuel through the fuel line is controlled by a flow valve adapted to block the flow of fuel to the nozzle at the end of a burn cycle in the operation of the system.
In burner control systems of the foregoing general character the regulating valve may be constructed so that air which may have accumulated in the system between burn cycles can be purged from the pump so as to avoid an air lock in the pump. One such regulating valve includes a passage bypassing the valve seat and connecting directly to the line leading from the valve to the burner nozzle so that air may be purged from the pump through the nozzle at the start of a burn cycle.
Another similar burner control system includes an ignition control circuit similar to that disclosed herein and, specifically, includes a control thermostat adapted to initiate the burn cycle in response to a demand for heat. When the circuit is made by closing contacts in the thermostat, a motor driven pump is actuated and pressurized fuel is driven by the pump through the regulating valve toward the nozzle. At the nozzle, the fuel is ignited by an igniter responsive to an ignition transformer. The latter is located within the ignition control circuit and is energized at the start of a burn cycle to provide the spark for the igniter to light the fuel. After the fuel is ignited, a light sensitive cell produces a signal in the control circuit to actuate a switching transistor and thereby cause the ignition transformer to de-energize.
In the operation of this type of burner control system, it is desirable to provide a means for blocking the flow of fuel from the regulating valve to the nozzle in the event that the fuel pressure drops below a desired operating pressure to a pressure level at which sufficient fuel may still pass through the regulating valve to maintain a flame that can be sensed by the cell.